Electric and electronic equipment utilized in industrial processes, switchgear and similar uses is generally enclosed in a casing of metal, usually some form of apparatus cubicle. The casing or the cubicle is utilized, inner alia, as a frame for internal installation of electric components, but also as protective casing for the electric equipment with respect to the influence of dust, moisture, aggressive agents, etc., as well as semiprotection for reasons of personal safety. In connection with this enclosure, the problem arises regarding the removal of heat emitted by the components present in the cubicles by the power developed in these components.
Thermal dissipation may be arranged in many ways, for example by radiation from the walls of the cubicles themselves, aeration of the cubicles by self-convection with the aid of ventilating openings, aeration with the aid of fans and filters, forced aeration by way of heat exchangers and conditioning by means of refrigerating machines.
If cooling is performed by ambient air, treatment of the air in the form of, for example, cleaning or drying may be necessary in those cases when the cubicles are located in a fouled or moist environment. Such cleaning may comprise filtering of the air or the removal of corrosive gases from the ambient air before this is supplied, in cleaned form, to the interior of the cubicles for cooling of the components located there. A number of different partial solutions for cleaning or treating air in the above-mentioned manner in individual apparatus cubicles for the purpose of removing excess heat from the cubicles are known. Such single-cubicle solutions are described, inter alia, in the patent documents EP,A3, 57 411, FR,A1,2 568 712 and JP 58-241 936.
In switchgear or other types of industrial plants where the electric equipment is extensive, it may be required that a number of cubicles assembled into a series of cubicles are arranged. A cubicle series of this kind is generally designed as a series of cubicles arranged in one or more rows with the individual cubicles placed side-by-side close to each other. Upon removal of heat from electric equipment in a cubicle series of the above-mentioned kind, single-cubicle solutions according to the above are not applicable. Providing each individual cubicle with its own air treatment unit cannot be justified from an economical point of view. Instead it is common to use an air treatment plant, also called a conditioning plant, to cool, moisten, dry or clean the air in the entire room where the cubicles in a series of cubicles are stored. With this method it is possible to achieve the desired cooling or cleaning of air to the electric equipment in the cubicles. The method can also be supplemented with fans in the individual cubicles to prevent the formation of stationary hot air zones inside the cubicles.
Treating all the air in a room to attain the desired effect with respect to, for example, the cooling requirement is not a good solution. The air volume that has to be treated is large, which means that the air treatment plant must be dimensioned for an air volume which is many times larger than the air volume which really passes the apparatus cubicles for cooling. This renders the air treatment plant more expensive than necessary. Another difficulty is that the room climiate must be adapted to human needs, since personnel may be present in the rooms mentioned. In this way it is not possible to optimize, for example, air temperature or air composition according to the primary requirements of the electric equipment. Treated air supplied to the room where the apparatus cubicles are erected is normaally varied within an interval of a couple of degrees above or below room temperature.
It is known that as large a percentage as 60-70% of normal operating environments for electric and electronic equipment in certain industries as, for example, paper and pulp industries, are so corrosive that they have a marked influence on the reliability of service and the service life of the equipment. Currently, therefore, this problem is often solved by air treatment comprising chemical filtering of the air in the whole of the room where the electric equipment in question is located, which entails treatment of a disproportionately large air volume.
It is also known that the service life of certain components of semiconductor type is greatly temperature-dependent. For these components, as low a temperature as possible in the immediate surroundings of the component is therefore desired. For electric equipment such as apparatus and electric busbars, the allowed working temperature is normally maximized in dependence on the temperature durability of the conductors and/or the insulating materials. The working temperature is dependent on both the immediate ambient temperature and the self-heating of the apparatus during normal loading. An increase of the temperature also provides an increase of the resistance of electric conductors in the equipment, which results in increased power output and a further increase of the temperature.
Swedish Patent No. 467,945 describes a method of treating the air in a series of adjacently located electrical apparatus cubicles, which are closed in relation to the surrounding air, by means of an air treatment unit common to the cubicles in order to reduce the air quantity treated. The method for air treatment comprises passing cleaned and cooled, possibly also hydrated or dried air, from an air treatment unit via a common channel and further via parallel branch Pipes with pressure-regulating devices for regulating the air flow, directly to each individual apparatus cubicle, these apparatus cubicles being adapted to receive the treated air, distribute the air for cooling purposes over electric equipment present in the cubicles, the distributed air being adapted to be collected and returned, via connections arranged between the cubicles, to the air treatment unit where an extra intake for ambient air is adapted to supply extra air to the air treatment system in order to create an overpressure in the system while at the same time replacing an air loss caused by a leakage flow of air out of the cubicle series. The direction of the air current through the system may be changed.
In all cooling of electric equipment according to the above, it is desirable that the cooling air be primarily directed towards regions or components where the cooling requirement is greatest or gives the best effect. As an example, it can be mentioned that in switchgear cubicles where the electricity supply of the cubicles is arranged by means of multiphase lanes (or paths) of busbars in the form of copper busbars, extending through the cubicles, the greatest heat generation takes place in the mentioned lanes of busbars. This problem can be avoided by a reduction of the allowed currents through the electric busbars or by increasing the flow areas of the busbars, which in turn entails increased material consumption and increased costs. Consequently, it would be desirable to guide the cooling air passed into the cubicles in a more efficient way, making it possible to increase the rated currents for cubicles or apparatus in cubicles while maintaining the amount of coolinq.
Swedish Patent No. 449 150 describes semiprotection for lectric busbar internally in electric switchgear cubicles. This patent illustrates grooves or boxes which surround both horizontal and vertical busbars, the grooves also constituting protection against unintentional contact. By their shape, these protective grooves form channels which, in a series of cubicles, are naturally interconnected to form a coherent system of interconnected channels extending through the entire cubicle series, these channels surrounding the busbars located in the respective cubicles. The invention disclosed in this patent shows a method of utilizing the above-mentioned already existing channels to distribute cooling air to switchgear cubicles in a more efficient way.